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Welcome to Sigmafield

Edit: This post originally appeared on my WordPress blog on September 20, 2009. I present it here in its original form.

John Tukey’s preface to Exploratory Data Analysis begins with a useful rule, “It is important to understand what you can do before you learn to measure how well you seem to have done it.” When I decided I wanted to start a blog concentrating on statistics, R, and Emacs, I thought I had better learn first what I can do to make the process of generating content easier. Here, as a meta first post, I present how I used Emacs, R, and other technologies to produce the output you are reading here.

Emacs, ESS, and org-mode

I use Emacs for everything I can. I started learning it as a graduate student in Statistics in order to use the ESS package. ESS lets you run R within Emacs, which is really nice for developing programs and performing data analysis interactively. I have discovered many Emacs packages through the years, but lately I have been learning the excellent org-mode package. Org-mode is designed so that you can get started with very minimal knowledge of its capabilities. You can ignore the more complicated aspects of it if you do not need them, and still have a great system for general organizational tasks and note taking. I think it is worth learning Emacs just so you can use org-mode!

Since I am so familiar with Emacs, and work in it daily, I really wanted to use it to write posts. Ideally, I would like to write my blog entries in org-mode, and be able to use in-line R code. The text and R code should be output to HTML and published to my blog. This HTML generation is possible because org-mode has a fantastic feature that exports to various formats, including HTML. This is beneficial since then all of my headlines, lists, tables, and source code markup in org-mode will be carried over to the HTML automatically.

Using the tools already available for Emacs, creating the HTML turned out to be much easier than I initially thought. The vast majority of the time preparing this was spent learning about those tools, and figuring out how to combine them in the right way to accomplish what I wanted to do.

To summarize, my goals were to:

write blog content in Emacs

use org-mode to manage content

be able to include R commands, output, and graphics easily

automatically syntax highlight the R commands and output

automatically syntax highlight other source code (e.g., elisp)

generate HTML automatically directly from Emacs

R, Sweave, and the ascii package

I really enjoy using R. Since I plan to write about statistics, and especially statistical computing, I imagine many of my posts will contain R code. R comes with an interesting function called Sweave. Sweave allows you to incorporate R commands within a document you are writing wrapped in a special syntax, see some demos. So you might be writing some or HTML and interweaving R code. After you run the Sweave function using the source (e.g., HTML) document as the input, a new file is created that replaces the R code with the results of the commands. This might sound simple, but it leads to a very powerful model for report generation and reproducible research. My goal was to somehow get publishable HTML from a source org-mode file after running Sweave on it. For example, say I want to generate 100 samples from a normal distribution with mean 10, and summarize the results.

I do not want to have to actually type any of the summary output, of course, but I also don’t have to even copy and paste it. What I can type is the R code to produce the output, and wrap it in Sweave syntax, like this:

<<>>=
x <- rnorm(100, mean = 10, sd = 5)
summary(x)
sd(x)
@

When I prepare this post for publishing, Sweave will run the R code and insert the output in place of the Sweave commands. I have wrapped the Sweave syntax in org-mode’s special BEGIN SRC construct, so that when I export to HTML, org-mode will properly syntax highlight the output using the htmlize package, as inspired by this post on using the htmlize package with Erlang. The only elisp I had to write was the following.

All the first function is doing is running an input file (an org-mode file) through Sweave with the RweaveAsciidoc driver found in the R ascii package. It basically just puts in the R output as plain text, as opposed to code or HTML.

The rest of the elisp function manipulates the output in some trivial ways. The explanation for the replacement of the four dashes is that the RweaveAsciidoc Sweave driver produces the dashed string both before and after the R output as a visual offset, since asciidoc uses that as a markup indicator. I did not need that, since my output will not be fed through asciidoc, but rather the org-mode HTML exporter, so I simply replace the dashes found at the beginning of a line with the empty string. The last trick I had to do was to replace the R syntax highlighting with R-transcript syntax highlighting, since the results of Sweave are essentially a transcript of the R commands entered, not the actual R code. Finally, the resulting HTML produced by the org exporter has its pre tags modified with custom colors and font size.

What is left to do?

There are a few loose ends that I didn’t have time to clean up yet. I would like to modify my Lisp function to work on regions if mark is set and transient-mark-mode is enabled. As of now, it just works on the whole buffer. The idea would be to have an org-mode file, say blog.org, that would have a top-level headline for each entry. You could then highlight that entry and publish it. I realize this is fairly trivial to implement, but it is not done yet.

I also want to investigate the publishing feature of org-mode, and see if there is any value add to using weblogger mode in Emacs. Using that, I could have a full Emacs solution to posting new entries, without even having to go into WordPress to paste HTML as I have done now. As an aside, I found longlines-mode in Emacs very useful for writing this post in org-mode, so that there are not newlines in random spots when the HTML is produced.

I have not tested how plotting from R works in this system. It would be great to be able to generate in-line graphics in my posts using R commands to construct plots.

Finally, it looks like there is a really interesting project on worg called org-babel that will allow not only weaving of R, but many other languages including Ruby, elisp, and shell scripts, turning org-mode into a platform for literate programming. I also just saw blorgit, a blogging engine in org-mode that makes use of the git version control system.

My function provided above should work if you have a recent version of org-mode, R, ESS, and the ascii package installed on your system. I have bound the function to F5 on my keyboard, so just hitting F5 in my org-mode buffer will create an HTML buffer and copy its contents to the kill-ring for pasting into WordPress.

Conclusion

When I started this process, I assumed I would have to write at least a few elisp functions, and possibly some extensions to org-mode, perhaps even an Sweave driver. After thoroughly examining the available tools, I ended up only having to write, in effect, one lisp function, and that is only a utility function to automate the combination of solutions I found. The moral is that while often times you will have to write your own functions to get the exact behavior you are after, it does pay to really research what is out there already. I found a solution to my problem, org-mode, that allows a much more flexible framework for extensions and has been thoroughly tested. I now get to enjoy the benefits of whatever future enhancements org-mode comes up with, including extensions by other org-mode users. In particular, the org-babel functionality looks very promising to replace or augment some of my work here. So before you write your own packages, research what others have already done. At the very least, you’ll know what value you are adding by doing it your own way, which is the lesson I took away from Tukey’s rule.